The present invention relates to apparatus for the precision placement of electronic components on a hybrid circuit substrate and, more particularly, to the placement of small articles such as semiconductor chips, capacitor chips and integrated circuit chips on a ceramic substrate which has been preprinted with a thick film conductor pattern.
As the name suggests, hybrid circuits are a combination of discrete and integrated circuit techniques. As in integrated circuits, conductors, resistors and conductive lands are printed on a ceramic substrate. In thick film technology, the printed elements are generally several mils thick. Then discrete chips are precisely positioned over the conductive lands and subsequently bonded in position in a manner to complete the electrical circuit. The printed conductor lands provide a pattern which precisely matches to the corresponding conductive portions of the chips that connect to the circuit elements within the chip as by solder. The bonded chips and substrate, with an exposed lead frame, are frequently encapsulated in toto in a potting compound for protection against physical and environmental damage. Use of unencapsulated chips on the circuit board allows for the manufacture of physically smaller circuits than those where discrete components which have already been encapsulated have their leads inserted into circuit boards fired with receiving connectors or into predrilled holes wherein the leads are subsequently cut and clinched. A primary advantage of chips is their small size, some being nearly microscopic. Chips in the order of 0.030 by 0.030 inches square and 0.010 thick and solder connection portions and conductor lands in the order of 0.005 inches in height and width, and spaced apart by similar distances, are not uncommon. Nevertheless, for the hybrid circuit technique to be successful, the small chips must be positioned and oriented such that when placed on the substrate, all solder connection portions and lands are properly connected without error. This requires a high degree of precision in positioning which was achieved in early development of these techniques by human operators using microscopes and tweezers.
The need for automatic, rapid, precise, repeatable and low cost means to position and bond chips on substrates was apparent if the burgeoning requirements of mass production in the electronics industry were to be met. Generally speaking, in the apparatuses which have been developed in the past, the chip or other small component, e.g., beam leaded components, are picked up by a hollow probe device which is connected to a vacuum source. When the probe touches the upper flat surface of the chip, the vacuum within the probe holds the chip against the probe end. The chip is then raised, translated in X and Y to the appropriate location above substrate, and lowered in Z onto the substrate. Prior attempts have been made to improve the precision of placement of the components onto the circuit board by combining centering fingers with the vacuum probe. Thus, while the probe supports the component by vacuum, the fingers center the component relative thereto prior to placement. Permanent bonding of chip to substrate is accomplished in some systems while the probe continues to hold the chip. In other systems, the conductive lands are pretreated with some form of tacky adhesive or soldering flux. The probe gently presses the chip surface into the tacky adhesive so that electrical contact is made with the conductive lands. Then the vacuum within the probe is released and the chip remains adhered to the substrate as the probe is withdrawn. A positive gas pressure within the probe is sometimes used to separate the chip from the probe.
In one form of the prior art, the substrate and the chip are both separately, fixedly and precisely oriented and located. A transfer mechanism, usually utilizing a vacuum probe as described above, travels an invariable, repetitive path to pick up the chip and place it at one selected position on the substrate. Then, a new substrate and new chip are fed into their respective positions and the operation repeats. In another form, the chips start out with a degree of disorientation, for example, at random in a vibratory feeder bowl. The feeder bowl, in the known manner, operates to bring each chip in turn to a precise position. From that point, the design is similar to the first category; although additional steps to angularly orient the chip may be required intermediate the feeder bowl and the precisely located substrate. Still other prior art has combined these two categories.
In the device of U.S. Pat. No. 4,611,397, components are successively placed by a hollow pick and placement spindle having motion in the X-Y and Z planes. The spindle, using a vacuum, picks up components individually from a plurality of precisely fixed input stations, e.g., component trays, racks, feeder bowls, behind the machine and delivers them to varied locations on the substrate until the component placements have been completed. To assure precision placement of components, the substrate edges and the spindle housing provide X-Y reference points, and pivoted fingers attached to the spindle homing center the chip on the spindle while correcting for slight misorientations about the Z-axis i.e., less than 45.degree., prior to placement, so the chip need not be precisely positioned at the input station for selection. Additionally, the support for the centering fingers is rotated about the vacuum probe axis, while the fingers are closed on the component, to provide control of the chip during angular orientation as the circuit board layout requires.
In U.S. Pat. No. 4,458,412, a carousel provides random vertical supply of taped components to a feeder assembly which feeds individual chips onto a nozzle of a turret-type vacuum head at a pick-up station. The turret-type head has four nozzles spaced 90.degree. apart about the central axis of the head. As the turret is rotated, a chip is transported by a nozzle sequentially from the pick-up station to a centering and testing station, a centering and orienting station, and a placement station. Located between the testing and orienting stations is a chip removal station for ejecting defective or inverted chips. Sensors are located at the adhesive and placement stations to detect defective P.C. boards so that they may be bypassed. A controller, such as a digital computer, provides additional monitoring and controls the operation of the machine.
None of the prior art teaches a turret with multiple spindles thereon whereby the turret addresses one or more supply stations to load the spindles and then translates to a circuit board to place the components selectively at various points on the circuit board.